The present invention relates in general to substrate manufacturing technologies and in particular to an apparatus for the deposition of a conformal film on a substrate and methods therefor.
In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited. Control of the transistor gate critical dimension (CD) on the order of a few nanometers is a top priority, as each nanometer deviation from the target gate length may translate directly into the operational speed and or operability of these devices.
In an exemplary plasma process, a substrate is coated with a thin film of hardened emulsion (such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing parts of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck. An appropriate set of plasma gases is then flowed into the chamber and struck to form a plasma to etch exposed areas of the substrate with a particular topography.
A common method of etching is called RIE (reactive ion etching). RIE combines both chemical and ion processes in order to remove material from the substrate (e.g., photoresist, BARC, TiN, Oxide, etc.). Generally ions in the plasma enhance a chemical process by striking the surface of the substrate, and subsequently breaking the chemical bonds of the atoms on the surface in order to make them more susceptible to reacting with the molecules of the chemical process. Since ion etching is mainly perpendicular, while the chemical etching is both perpendicular and vertical, the perpendicular etch rate tends to be much faster than in then horizontal direction. In addition, RIE tends to have an anisotropic profile.
A common substrate manufacturing method that uses RIE is called dual damascene, in which dielectric layers are electrically connected by a conductive plug filling a via hole. There are generally two approaches manufacture dual damascene substrates: via-first and trench first. In one example of the via first methodology, the substrate is first coated with photoresist and then the vias are lithographically patterned. Next, an anisotropic etch cuts through the surface cap material and etches down through the low-k layer of the substrate, and stops on a silicon nitride barrier, just above the underlying metal layer. Next, the via photoresist layer is stripped, and the trench photoresist is applied and lithographically patterned. Some of the photoresist will remain in the bottom of the via and prevent the lower portion via from being over-etched during the trench etch process. A second anisotropic etch then cuts through the surface cap material and etches the low-k material down to a desired depth. This etch forms the trench. The photoresist is then stripped and the Silicon Nitride barrier at the bottom of the via is opened with a very soft, low-energy etch that will not cause the underlying copper to sputter into the via. As described above, the trench and via are filled with a conductive material (e.g., aluminum (Al), Copper (Cu), etc.) and polished by chemical mechanical polishing (CMP).
An alternate methodology is trench-first. In one example, the substrate is coated with photoresist and a trench lithographic pattern is applied. An anisotropic dry etch then cuts through the surface hard mask (again typically SiN, TiN or TaN) followed by stripping the photoresist. Another photoresist is applied over the trench hard mask and then the vias are lithographically patterned. A second anisotropic etch then cuts through cap layer and partially etches down into the low-k material. This etch forms the partial vias. The photoresist is then stripped for trench etch over the vias with the hard mask. The trench etch then cuts through the cap layer and partially etches the low-k material down to desired depth. This etch also clears via holes at the same time stopping on the final barrier located at the bottom of the via. The bottom barrier is then opened with a special etch.
However, escalating requirements for high circuit density on substrates may be difficult to satisfy using current plasma processing technologies. For example, sub-micron via contacts and trenches may have high aspect ratios, low-k films and complex film stacks may be sensitive to small changes in plasma recipes are used, substrate feature sizes and critical dimensions may be decreasing, and substrate topography complexity may be increasing.
One method of mitigating these effects may be the deposition of conformal films. In general, a conformal film is a relatively thin layer (often just a few atoms in thickness) that substantially covers or coats exposed surfaces of the substrate with a relatively uniform thickness. That is, the film “conforms” to the feature topology of the substrate, much like a thin coat of spray paint. In general, conformal films may be useful to smooth out undesirable roughness on surfaces during etching processes (e.g., dual damascene, etc.), such as the irregular sidewalls (e.g., line-edge roughness, standing wave patterns, etc.) typically produced by photoresist patterning (e.g., 193 nm, etc.).
A common method of producing a highly uniform conformal film may be ALD (atomic layer deposition). In a typical ALD process, the conformal film is deposited on a substrate one atomic layer at a time using pulses of gas. Once deposited, the ALD process automatically stops. That is, the process is self-limiting. However, an ALD process is typically carried out from about 200° C. to about 400° C., making the process unsuitable in a photoresist etching process. In general, photoresist generally disintegrates at temperatures above 150° C. In addition, ALD also tends to be very time consuming, since several atomic layers usually need to be added. For example, creating a conformal film on a particular substrate with a thickness of 1000 Å may take over 100 minutes. Furthermore, ALD is also limited in the materials that may be deposited. For example, ALD usually cannot deposit carbon, hydrocarbon, and/or fluorocarbon films, which may be useful in plasma processing.
Another method of producing a conformal film may be chemical vapor deposition (CVD) in which deposited species are formed as a result of chemical reaction between gaseous reactants at elevated temperature in the vicinity of the substrate. In addition, unlike ALD, the deposition process may be fairly rapid. For example, creating a conformal film with a thickness of 1000 Å may take about 30 seconds. However, like ALD, CVD reactions are typically carried out at high temperature, often above 400° C., making CVD also unsuitable for use in a photoresist etching process. Furthermore, since a CVD reaction tends to complete before the process reactants are able to substantially diffuse along substrate surfaces, high-aspect ratio structures are generally not penetrated, and rough substrate surface areas tend to remain. That is, CVD tends to achieve a relatively low level of conformality in complex substrate topographies.
In view of the foregoing, there are desired apparatus for the deposition of a conformal film on a substrate and methods therefor.